Method at vehicles having a lifting device for compensating departures in the position of loads on the lifting device relative to the frame of the vehicle

Abstract

The present invention relates to a compensating method applicable to vehicles having a lifting device made up of a mast (4) and vertically adjustable load carrier (5) provided on the mast. The method is for compensating departures in the position of loads (8, 9), preferably goods on loading stools or pallets, on the load carrier (5) relative to a frame (2) of a wheel driver vehicle (1). Loads (8, 9) of different weight when lifted to various heights deflect the mast (4) outwards in various degrees from an unloaded position. The vehicle (1) is adapted to repeatedly deliver loads (8, 9) on the load carrier (5) at different levels (12, 13, 14) in a storage system (11) and in predetermined delivering positions (P3) on each such level (12, 13, 14). A drive-up length (L o ) corresponding to moving the vehicle (1) without a load (8, 9) from a reference point (R2) to a delivering position (P2) has been determined. In order to provide quick and safe compensation of deflections, the invention determines the size (Δ1) of the outward deflection of the mast (4) is and the vehicle (1) is operated to move from the reference point (R2) towards the delivering position (P2) by length (L last ) corresponding to the determined drive-up length (L o ) reduced by a partial length (Δ1) which depends on the outward deflection of the mast (4).

I claim: 
     
       1. A method of compensating for departures in the position of loads on a lifting device relative to a frame of a vehicle, the vehicle having control means for being controlled by reference markings on a floor and being adapted to repeatedly deliver loads on a load carrier to different levels in a storage system, said method comprising the steps of: (a) predetermining a delivering position (P3) along an axis corresponding to each storage level;   (b) measuring with the control means on the vehicle a drive-up length (10) corresponding to a length required to move the vehicle without a load from a reference point on the floor (R2) to an unload delivering position (P2), the unload delivering position (P2) allowing a vertically adjustable load carrying means attached to a mast to deliver loads to the delivering positions (P3) on the storage levels;   (c) at a loading position (P1), loading goods on the vertically adjustable load carrying means provided on a mast of the vehicle and lifting the load carrying means on the mast to the desired vertical level;   (d) measuring stress on the load carrying means and activating a calculating means to determine outward and downward deflection of the mast under load at the desired vertical level;   (e) while maintaining the mast in the deflected position, moving the vehicle from the loading position (P1) to the reference point on the floor (R2) and using the vehicle control means, moving the vehicle from the reference position toward the unload delivering position (P2) by a length corresponding to the drive-up length (L0) reduced by an amount depending upon the outward deflection of the mast and moving the vertically adjustable load carrying means upward by an amount depending upon the downward deflection of the mast.   
     
     
       2. Method according to claim 1 comprising positioning the reference point (R2) at a location on a predetermined path of travel of the movement of the vehicle toward the delivering position (P2) such that the vehicle, when situated in a predetermined relationship with said reference point (R2), is in a load lifting position (P1) relative to said delivering position (P2), whereby the load carrier, which is elevated during load lifting, has clearance to the storage system for receiving the load when the vehicle is in said load lifting position (P1). 
     
     
       3. Method according to claim 1 further comprising determining the size of the outward deflection of the mast and of the downward deflection of the load carrier by sensing the strain of the load on those parts of the load carrier situated between load carrying members and members thereof cooperating with the mast. 
     
     
       4. Method according to claim 1, comprising sensing the strain of the load on the load carrier by means of a thread stretching indicator. 
     
     
       5. Method according to claim 1, wherein the load carrier has two lifting forks comprising sensing the strain of the load on the load carrier by means of a thread stretching indicator provided in the base of at least one of the lifting forks. 
     
     
       6. The method of claim 1 further comprising the steps of: moving the vehicle using the vehicle control means from the reference point on the floor (R2) an amount equal to the drive-up length (L0) and subsequently moving the vehicle in an opposite direction by an amount compensating for outward deflection of the mast.